1. Field of the Invention
The present invention relates to a steering assist system for a motorcycle. In particular, it relates to a steering assist system including an actuator that gives a steering torque to steering.
2. Description of the Related Art
A variety of control techniques have been developed to further improve the running stability of a motorcycle. A known example of techniques to improve the running stability is a steering damper. Japanese Patent Application Publication No. 2007-125917 proposes another example of such techniques in which an actuator is provided to actively control the steering system (specifically, the rear wheel).
In the technique disclosed in the above-mentioned patent document, the steering of the rear wheel is based on the target steering angle and the delayed steering angle for the rear wheel that are determined in accordance with the vehicle speed and the roll rate.
Incidentally, motorcycles are inevitably more prone to external influences, such as an irregular ground surface and a crosswind, than four-wheel automobiles. The external influences cause wobbles in the steering, and it is desirable to reduce the steering wobbles of motorcycles.
The active-control technique in the example of the above-mentioned patent document is basically the position control of the steering angle. Accordingly, the technique is applicable to the controlling of the rear wheel, but it is actually difficult to apply the technique to the front wheel that is directly operated by the rider.
In addition, the technique in the example of the above-mentioned patent document basically aims to improve the performance at the time of changing lanes or of giving a turn. Reducing the steering wobbles caused by the external influences is out of concern to the above-mentioned patent document.